Fuel cells are expected to be commonly used in future since they have high power generation efficiency and present little burden on the environment as the reaction product is only water in principle. Among them, polymer electrolyte fuel cells have high output densities and thus are expected to be widely used as distributed power generation systems for automobiles, mobile power generation systems and domestic co-generation systems.
A polymer electrolyte fuel cell is usually composed of a cell wherein an electrically conductive separator provided with gas flow paths is disposed on each side of a membrane/electrode assembly comprising a cathode having a catalyst layer and a gas diffusion layer, an anode having a catalyst layer and a gas diffusion layer and a polymer electrolyte membrane disposed between the catalyst layer of the cathode and the catalyst layer of the anode.
As the gas diffusion layer, a gas diffusing base material having carbon fibers integrated (such as carbon paper, carbon cloth or carbon felt) is usually employed. However, if carbon fibers become fluffy on the surface of the gas diffusing base material, such carbon fibers are likely to pierce the catalyst layer adjacent to the gas diffusion layer and further pierce the polymer electrolyte membrane, thus causing shortcircuiting, etc.
For example, the following one has been proposed as a membrane/electrode assembly whereby a damage of the polymer electrolyte membrane by carbon fibers of the gas diffusion layer is prevented.
A membrane/electrode assembly having a protective adhesive layer comprising electrically conductive carbon particles (such as Ketjen black or acetylene black) and a fluorinated ion exchange resin, between the catalyst layer and the gas diffusion layer (Patent Document 1).
However, in such a membrane/electrode assembly, if the length of fluffy carbon fibers on the surface of the gas diffusing base material is longer than the thickness of the protective adhesive layer, such carbon fibers are likely to pierce through the protective adhesive layer into the polymer electrolyte membrane. Further, such a protective adhesive layer has small pores and poor water drainage and thus is susceptible to clogging (flooding) of pores due to condensation of steam.